To reduce dependence on non-renewable fossil energy sources, the investment and need of alternative energy sources, such as solar-photovoltaics, are growing rapidly. Photovoltaics (PV) generate electrical power by using solar cells, and dramatically reduce the emissions of greenhouse gases (GHG). Through 2006 to 2011, photovoltaics grew the fastest of all renewable technologies with operating capacity increasing an average of 58% annually. However, the cost of manufacturing solar-grade silicon (SoG-Si) for high-efficiency solar energy production represents a major barrier to achieving the industrial goal for solar power of $1/Wp (watt at peak exposure) which would enable widespread grid parity. The current contract price of silicon to PV manufacturers is $50-$60/kg, with the spot market in 2007-2008 showing prices as high as $300/kg. This makes the development of low cost and environmentally friendly manufacturing of high purity silicon very important.
According to existing methods, over 90% of silicon produced requires a purification process, which involves chlorination, distillation and chemical vapor deposition, after metallurgical-grade (MG) Si is manufactured by carbothermic reduction of silica. One such process, known as the Siemens process, includes multiple steps, has low capital utilization, but is extremely energy-intensive, and produces much higher product purity (10 to 11 nines) than what the solar cells need (6 nines). The Siemens process has been the primary method of silicon production. In order to reduce the high cost of silicon production, several alternate processes of silicon production are being developed, and some of them have achieved varying levels of success. These include, reduction processes in fluidized bed reactors, carbothermic reduction of high-purity silica, slag/crystal refining, liquid silicon electro-refining, among others. However, disadvantages of these processes are expensive raw materials pre-processing, detrimental environmental impact, substantial energy requirements and relatively low yields.
In view of the above, there is a need for an environmentally friendly and cost effective method of producing silicon.